Conventional communication systems often require a form of channel selection (or isolation filtering) in the receiver signal path. For example, in a television system, a single desired channel must be accurately selected from potentially hundreds of channels. Likewise, in a cellular receiver, the handset must first isolate and filter out signals from other systems such as pagers or incompatible competing voice services. Such isolation of signals mitigates the effect of blocking/desensitizing out-of-band signals and aids in maximizing overall receiver performance.
Such conventional filters typically are implemented with discrete, high-performance external components (e.g., surface acoustic wave or ceramic filters), owing to the need for accurate filter response and center frequency, as well as stability over time and temperature. However, such precision external components can be large and expensive. U.S. Pat. No. 5,822,687 and U.S. Pat. No. 4,685,150 disclose methods for accomplishing electronic filter tuning.
It may be desirable to implement inexpensive, low-tolerance external components coupled with highly integrated silicon processing to compensate for channel equalization, process variation, inaccuracies and drift.